All roads in Estonia are officially prefixed with T, and the Põhimaanteed, Tugimaanteed and Kõrvalmaantee (I did what you want me to do in the CHM-TM intermission, and then reversed it when I found that I was wrong here) - cf the Dutch N roads where we have two systems of roads that are all N<number>.
The first two digits on Kõrvalmaantee refer to the county and are administrative (so that they are unique numbers across the country) - they were always on OSM, but heavy research when doing the E roads meant I stripped them down to three-digit, having initially had 5.